1. Adds map plot of model output to priors app

[gareth-j]

• Summary of changes
  Adds ability to plot predictions data onto a leaflet map.

• Please check if the PR fulfills these requirements

• All code checks passing - styler run over code
• Closes can we change the name of "interactive_priors" to "model_builder" #151
• Vignettes updated/added
• Added an entry in the latest CHANGELOG.md file if fixing a bug or adding a new feature
• Any new libraries added to DESCRIPTION

[XueqingYin]

Here are a few changes that need to be made.

1. In my opinion, only the plot of “mean_post + fixed_mean” and the plot of “mean_post” hold statistical significance.

• The plot of “mean_post + fixed_mean” means we are plotting the predicted mean fields on the raw data scale. It corresponds to the code:
  z <- base::exp(base::as.numeric(A_proj %*% var_a[1:mesh$n]) + base::sum(var_b))

• The plot of “mean_post ” means we are plotting the random effect fields. It corresponds to the code: z <- var_a[1:mesh$n]
  After computing “z” properly, we can then plot using create_raster()

2. It would be helpful to provide explanations for the variables "mean_post" and "fixed_mean" respectively, maybe under the "Help" tab:

• “mean_post” represents the random effect values at mesh nodes

• “fixed_mean” denotes the fixed effects values, i.e., the regression parameters values

3. Depending on the data type, the calculation of z is a bit different. If plotting “mean_post + fixed_mean”, then it should be
   z <- base::exp(base::as.numeric(A_proj %*% var_a[1:mesh$n]) + base::sum(var_b)) for Poisson data.
   z <- base::as.numeric(A_proj %*% var_a[1:mesh$n]) + base::sum(var_b) for Gaussian data
   If plotting “mean_post”, it should be z <- var_a[1:mesh$n] for both Poisson and Gaussian data

[XueqingYin]

It looks great, thank you @gareth-j. Is it possible to add a legend to the outputs map? Currently, the raster image doesn't have a legend, so we can't know which colors represent high values, which represents low values. Function leaflet::addLegend(pal = , values =, title = " ") should help with that.

[XueqingYin]

The legend looks good, thanks.